I'm not sure I understand your bug report. Can you give a step-by-step reproduction case, with expected and actual outcomes?
The Mixer Streaming Key have this format: "3359905-li45wtutdqml7utcvzefllbs4xuvk7uo". The 1st part is the Channel ID. If I copy and paste this kind of key on OBS, the streaming goes as expected. But, if I do the integration with Mixer, the stream key is modified by OBS losting its inicial numbers, becoming something as: "li45wtutdqml7utcvzefllbs4xuvk7uo". I can see this removing the integration and checking the Key on OBS. The key become invalid because lost the inicial numbers on the streaming key.